首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   30749篇
  免费   3868篇
  国内免费   30篇
  2017年   209篇
  2016年   292篇
  2015年   375篇
  2014年   458篇
  2013年   761篇
  2012年   789篇
  2011年   800篇
  2010年   558篇
  2009年   459篇
  2008年   698篇
  2007年   737篇
  2006年   706篇
  2005年   713篇
  2004年   686篇
  2003年   712篇
  2002年   718篇
  2001年   1889篇
  2000年   1865篇
  1999年   1466篇
  1998年   491篇
  1997年   492篇
  1996年   495篇
  1995年   436篇
  1994年   443篇
  1993年   441篇
  1992年   1100篇
  1991年   1093篇
  1990年   1081篇
  1989年   1040篇
  1988年   969篇
  1987年   916篇
  1986年   778篇
  1985年   757篇
  1984年   598篇
  1983年   522篇
  1982年   386篇
  1981年   354篇
  1980年   341篇
  1979年   570篇
  1978年   455篇
  1977年   419篇
  1976年   350篇
  1975年   465篇
  1974年   478篇
  1973年   421篇
  1972年   398篇
  1971年   315篇
  1970年   271篇
  1969年   251篇
  1968年   236篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
941.
942.
U. Mishra  D. C. Spanner 《Planta》1969,90(1):43-56
Summary The sieve plate pores of Salix caprea in preparations fixed in glutaraldehyde are normally found to be occupied by slime fibrils showing periodic banding such as occur in a number of other species. Arguments are put forward to suggest that the occurence of fibrils in this position is natural and not an artefact of preparation. The sieve tubes further possess prominent and persistent nucleoli showing a radiating structure of tubules. The endoplasmic reticulum often occurs in parietal stacks reminiscent of other species.This evidence is discussed in relation to the electroosmotic theory of translocation.This work formed part of that submitted for the degree of Ph. D. of the University of London by U. Mishra.  相似文献   
943.
944.
1. The maltase, isomaltase and invertase (sucrase) activities of solubilized mucosal preparations from human jejunum and ileum were studied with column chromatography on anion-exchange (diethylaminoethyl- and triethylaminoethyl-)cellulose and Sephadex G-200 gel. 2. On ion-exchange cellulose columns both kinds of enzyme preparations yielded two major disaccharidase peaks. The first peak contained maltase Ia (=isomaltase) and maltase Ib (=invertase). The second peak contained maltase II and maltase III. 3. On Sephadex G-200 gel columns jejunal preparations yielded the corresponding peaks as on ion-exchange columns, but the peaks appeared in the reverse order in the effluent. The ileal preparation studied yielded a single peak on gel columns, containing all the activities studied and eluted with the `void volume'. 4. Precipitation with ethanol did not affect the behaviour of the enzymes during ion-exchange chromatography. When gel filtration was performed after ethanol precipitation of the enzymes, however, two peaks were obtained also with the ileal preparation, and subfractionation of the invertase was obtained with both kinds of preparations. 5. The second peak from ion-exchange chromatograms, containing maltase II and maltase III, on concentration was found to have very weak isomaltase activity, probably exerted by these enzymes as such. This activity accounts for only about 1% of the total isomaltase activity of the mucosa. 6. The results support the concept of the specificity of the human small-intestinal disaccharidases previously described after heat-inactivation experiments. The subfractionation of the invertase that under certain conditions is seen on Sephadex G-200 columns appears most likely to be an artifact. Consequently the nomenclature for the human maltose-, isomaltose- and sucrose-splitting enzymes proposed by another research group after gel-filtration chromatography studies should be abandoned. It seems more logical to keep the nomenclature based on heat inactivation [maltase Ia (=isomaltase), maltase Ib (=invertase or sucrase), maltase II and maltase III] until increased knowledge about the specificity and structure of these enzymes makes possible a more rational nomenclature.  相似文献   
945.
946.
947.
948.
Zusammenfassung Bei einem Patienten mit multiplen Mißbildungen wurde eine Duplikation für die distale Hälfte vom kurzen Arm des Chromosoms 2 und eine Defizienz an einem C-Chromosom gefunden. In der Literatur sind vier Fälle mit ähnlicher Duplikation, jedoch jeweils einer klein n Defizienz am Chromosom 3 beschrieben worden. Ein Vergleich der klinischen Merkmale bei den fünf Patienten zeigt weitgehende Übereinstimmungen. Es wird gefolgert, daß die gleichartige Duplikation für das einheitliche klinische Bild der Patienten verantwortlich ist. Es wurden Chromosomenmessungen, Analysen der Replikationsmuster und Meioseuntersuchungen durchgeführt. Die Genloci für das Ss- und das Rh-System konnten von einer Lokalisierung auf dem duplizierten Segment ausgeschlossen werden.
2/C translocation in father and daughter: 46,XY t (2p-;Cp+) and 46,XX Cp+
Summary In a patient with multiple anomalies, a duplication comprising the distal half of the short arm of chromosome 2 and a small deficiency of a C-chromosome was found. Four other cases from the literature exhibit a similar duplication combined with a small deficiency each of chromosome 3. Comparison of the clinical pictures of the five patients revealed a conformity in the major features. It is concluded that the duplication is responsible for the uniform appearance of these patients. The studies performed include chromosome measurements, examination of replication patterns and meiosis. The gene loci for the Ss and Rh systems could be excluded from localization on the duplicated segment.


Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.  相似文献   
949.
U. Wolf  J. Klose  G. Oser 《Human genetics》1969,8(2):137-141
Zusammenfassung Kanarienvogel (Serinus) und Stieglitz (Carduelis) zeigen für das Enzym Glucose-6-Phosphat-Dehydrogenase in der Stärkegelektrophorese jeweils nur eine Bande, die aber verschiedene Positionen einnehmen. Interspecieshybriden beider Geschlechter wurden aus der natürlichen Kreuzung Kanarienvogel (f)xStieglitz (m) erhalten; die Identifizierung des Geschlechts der äußerlich ähnlichen Hybriden erfolgte durch Chromosomenanalyse. Die Hybriden zeigen in beiden Geschlechtern ein identisches Elektrophoresemuster, das die gleiche Zone umfaßt wie bei dem in vitro-Gemisch aus Gewebehomogenaten der Ausgangsarten. Entsprechende Befunde liefert die Analyse der 6-Phosphogluconatdehydrogenase. Hieraus ist zu schließen, daß beide Enzyme von autosomalen Genen determiniert werden.
Autosomal determination of glucose-6-phosphate dehydrogenase in birdsStudies on interspecific hybrids of serinus and carduelis (family: Fringillidae)
Summary The electrophoretic mobility of the single G-6-PD-band in Serinus and Carduelis is different. The natural cross Serinus (f)xCarduelis (m) results in viable hybrids of both sexes, as confirmed by chromosome analysis. The isoenzymes of G-6-PD are indentical in both sexes of the hybrids, exhibiting a broad diffuse pattern comprising the same zone as obtained from an in vitro mixture of parental homogenates. Related findings are reported on the enzyme 6-PGD. It is concluded that both enzymes are autosomally determined in these species.


Mit Unterstützung durch die Deutsche Forschungsgemeinschaft.

Wesentliche Teile dieser Arbeit werden von Herrn G. Oser als Dissertation der Medizinischen Fakultät der Universität Freiburg i. Br. vorgelegt.  相似文献   
950.
In a chromosome study on leucocyte cultures made in 13 patients treated with chlorpromazine, 15 treated with perphenazine, and nine treated with lysergide, a significantly higher frequency of gaps, breaks, and hypodiploid cells in the patients treated with perphenazine and lysergide occurred compared with the 41 controls studied. It is concluded that if some drugs can induce major chromosome abnormalities, and less toxic alternatives are available, the latter should be used in preference.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号